Blender 2.79b model export to Collada
The default Blender Exporter does not seem to be able to embed textures into Collada *.dae files (as of 2.79b).

It can however save textures alongside Collada files. To do that it has two sources of texture files.

Materials as texture source

See this video if you want to see it in action.

This is used when you select Materials in the Texture Options section of the Collada Export dialog.



The steps you need to make sure the texure is set, do the following:


Be sure that you are in Blender Render or Blender Game mode (you can switch back to another renderer after you set the texture)
1a. Select your object and go into the textures tab of the Properties Panel
make sure that you are editing the textures of the material
add at least one texture of type Image (you can add multiple textures and all will get saved)
set the image for the texture




UV Texture as texture source

See this video if you want to see it in action.

This is used when you select UV Textures in the Texture Options section of the Collada Export dialog.



The steps you need to make sure the texure is set, do the following:


Be sure that you are in Blender Render or Blender Game mode (you can switch back to another renderer after you set the texture)  
Select your object and go into edit mode
open a UV/Image Editor panel and set the image you want to export as the texuture (you can switch back into object mode and this image will persist as the one that will be exported).